Wildfires fanned by strong winds swept through northern California's wine country on Monday, killing at least 10 people, destroying hundreds of homes and businesses and forcing some 20,000 people to flee.

The deaths brought the official wildfire-related toll in California this year to 13, the greatest loss of civilian life from a single cluster of blazes in the state in a decade, state fire officials said.

Governor Jerry Brown declared a state of emergency for Napa, Sonoma and Yuba counties, encompassing some of the state's prime wine-making areas, as the blazes raged unchecked and engulfed the region in thick, billowing smoke that drifted south into the San Francisco Bay area.

A firefighter works to put out hot spots on a fast moving wind driven wildfire in Orange, California on October 9, 2017. MIKE BLAKE/REUTERS

He later extended the declaration to include four more northern California counties and Orange County in Southern California, and requested a U.S. presidential disaster declaration to support state and local firefighting resources.

Sonoma County bore the brunt of the fatalities, with seven fire-related deaths confirmed there, according to the sheriff's department. Two died in Napa County and one in Mendocino County, according to the California Department of Forestry and Fire Protection (CalFire).

Details of those deaths were not immediately available from state or local officials. But KGO-TV in San Francisco, citing unnamed California Highway Patrol sources, described one victim as a blind, elderly woman found in the driveway of her home in Santa Rosa, a town in Sonoma County.

Smoke rises as a wildfire burns in the hills east of Napa, California on Monday October 9, 2017. Michael Short/AP

The death toll could climb higher, said Brad Alexander, a spokesman for the governor's Office of Emergency Services. More than 100 people were treated for fire-related injuries such as burns and smoke inhalation, CNN reported.

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The toll marks a 10-year record for civilian wildfire fatalities in the state, dating back to 14 who lost their lives in a series of blazes that swept San Diego County and other parts of Southern California in October 2007, according to CalFire spokeswoman Janet Upton.

Ten people died in August 2008 in the Iron Alps Complex Fire in northern California's Trinity County, including a crew of nine contract firefighters from Oregon killed in a helicopter crash.

On Monday, thousands of firefighters battled wind gusts in excess of 50 miles per hour (80 km/h) that have rapidly spread 15 separate wildfires across some 73,000 acres (114 sq miles) in northern California since erupting late Sunday night, according to CalFire spokesman Daniel Berlant. About 1,500 homes and commercial buildings have been destroyed throughout the region, Ken Pimlott, director of CalFire, told reporters. Two hospitals were forced to evacuate in Sonoma County, state officials said.

A separate wildfire on Monday torched at least a half-dozen homes in the affluent Anaheim Hills neighborhood of Southern California's Orange County, forcing the evacuation of hundreds of residents, authorities said. That blaze erupted along a freeway off-ramp and spread quickly in gusty winds to scorch some 5,000 acres (8 sq miles) in a matter of hours, fire officials said.

Fear in wine country

Still, the situation there paled in comparison to one of the fiercer blazes in northern California, the so-called Tubbs fire, which charred about 27,000 acres (42 sq miles) in Napa and Sonoma counties, an area world-famous for its vineyards.

One evacuee, John Van Dyke, recalled standing in his pajamas near the 101 Freeway in Santa Rosa, watching a hillside in flames, when police pounded on his door in the mobile home park, telling him to flee.

"When I got in the car to leave, a whole section of the mobile park was in flames," he said. "It scared the hell out of me."

At least 5,000 people were under mandatory evacuation orders in Santa Rosa alone, accounting for about a quarter of the region's residents displaced by fires.

San Francisco authorities issued an air quality alert due to smoke from the fires, which residents said they could smell since early morning.

"You can't see anything, the smoke is very dense," Fred Oliai, 47, owner of the Alta Napa Valley Winery, told Reuters by telephone. He said he has not been able to get close enough to his vineyards since he was evacuated to see if flames reached his 90-acre property.

In addition to potential damage to vineyards from fire itself, experts say sustained exposure to heavy smoke can taint unharvested grapes, and Oliai said wine makers in the area are nervous.

"We got our grapes in last week, but others still have grapes hanging," he said.

The region threatened by fires overlaps an area accounting for roughly 12 percent of California's overall wine production by volume but also where its most highly valued grapes are grown, said Anita Oberholster, a professor of viticulture and enology at the University of California at Davis.

So far this year, some 7,700 wildfires in California have burned about 780,000 acres statewide as of Sunday, CalFire's Berlant said.

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